In advanced age, the performance of the heart is diminished and the susceptibility of the heart to ischemic injury is increased. Age- dependent alterations in myocardial Ca2+ regulation have been implicated as the cellular basis for both of these functional observations. There is now evidence indicating that agents that inhibit cardiac mitochondrial Ca2+ overload can significantly spare the myocardium from injury following bouts of ischemia. Our laboratory recently acquired preliminary evidence that are consistent with the idea that with progressive aging, mitochondrial in intact left ventricular cardiocytes have a greater propensity to take up Ca2+ when sarcoplasmic Ca2+ concentration is elevated. Such an age-dependent adaptation could be viewed as being positive insofar as an increase in mitochondrial Ca2+ uptake rate/capacity may represent a cellular mechanism to compensate for the well-known age-related diminution in sarcoplasmic Ca2+ clearance by the sarcoplasmic reticulum (SR). This type of adaptation, however, might also increase the risk of mitochondrial Ca2+ overload, particularly under conditions that challenge myocardial Ca2+ handling systems. The primary objective of this pilot project is to determine the effect of progressive age on mitochondrial Ca2+ uptake characteristics in intact rate LV cardiocytes. We propose to study myocytes isolated from F344xBN rats in young adulthood (8 mos), mature adulthood (16 mos), and in advanced age (32 mos). Fluorescence microscopy (fura-2) will be used to assess sarcoplasmic [Ca2+] dynamics and rapid solution switching techniques will be used to isolate and eliminate both SR and NaCa exchange (NaCaX) mediated Ca2+ removal mechanisms. To determine the contribution of the mitochondria to nonSR and nonNaCaX mediated Ca2+ removal from the sarcoplasm, we will use ruthenium red (25 nM) to suppress mitochondrial Ca2+ uptake and dihydrorhod-2AM to assess mitochondrial [Ca2+]. Our preliminary data clearly indicate that the capacity of nonSR-and nonNaCaX-mediated sarcoplasmic Ca2+ clearance increases in advanced age. If this reflective of an increase in mitochondrial Ca2+ uptake, then a strong case could be made that advanced age elicits intrinsic changes in mitochondrial Ca2+ handling. This may have profound implications with regard to our understanding of the cellular basis age-related losses in myocardial resistance to ischemic damage and to the regulation of oxidative metabolism in the aged heart.